Exercise stress echocardiography for the study of the pulmonary circulation

Abstract

Exercise stress tests have been used for the diagnosis of pulmonary hypertension, but with variable protocols and uncertain limits of normal. The pulmonary haemodynamic response to progressively increased workload and recovery was investigated by Doppler echocardiography in 25 healthy volunteers aged 19-62 yrs (mean 36 yrs). Mean pulmonary artery pressure ((Ppa)) was estimated from the maximum velocity of tricuspid regurgitation. Cardiac output (Q) was calculated from the aortic velocity-time integral. Slopes and extrapolated pressure intercepts of (Ppa)-Q plots were calculated after using the adjustment of Poon for individual variability. A pulmonary vascular distensibility alpha was calculated from each (Ppa)-Q plot to estimate compliance. (Ppa) increased from 14+/-3 mmHg to 30+/-7 mmHg, and decreased to 19+/-4 mmHg after 5 min recovery. The slope of (Ppa)-Q was 1.37+/-0.65 mmHg x min(-1) x L(-1) with an extrapolated pressure intercept of 8.2+/-3.6 mmHg and an alpha of 0.017+/-0.018 mmHg(-1). These results agree with those of previous invasive studies. Multipoint (pa)-Q plots were well described by a linear approximation, from which resistance can be calulated. We conclude that exercise echocardiography of the pulmonary circulation is feasible and provides realistic resistance and compliance estimations. Measurements during recovery are unreliable because of rapid return to baseline.

Figure 1

Source Doppler tricuspid regurgitation (TRV) and aortic flow (VTI-LVOT) signals at increased workload and derived mean pulmonary artery pressure (mPAP) and cardiac output calculations for a representative subject. The best fit for the mPAP-cardiac output relationship was linear with a slope of 1 L/min/mmHg and an extrapolated intercept of 9 mmHg.

Figure 2

Mean pulmonary artery pressure (mPAP) and cardiac output (Q) measurements at rest and at progressively increased workload in 25 healthy subjects. By best fit to a simple model of pulmonary vascular distensibility, a slight curvilinearity with convexity to the pressure axis can be seen in mPAP-Q relationships.

Figure 3

Poon-adjusted mean pulmonary artery pressure (mPAP) as a function of cardiac output (Q) measurements at rest and at progressively increased workload in 25 healthy subjects. The slope was 1.32 mmHg.min/L and the intercept 8.2 mmHg

Figure 4

Log mean pulmonary artery pressure as a function of log cardiac output measurements at rest and at progressively increased workload in 25 healthy subjects. Takeoff and plateau patterns can be identified in 14 and 11 subjects, respectively.